Electric discharge lamps



June 28, 1966 w. J. SCOTT 3,258,630

ELECTRIC DISCHARGE LAMPS Filed Jan. 25, 1963 as the vapour pressure on the other side,

United States Patent 3,258,630 ELECTRIC DISCHARGE LAMPS William Joseph Scott, Rugby, England, assignor t0 Associated Electrical Industries Limited, London, England, a British company Filed Jan. 25, 1963, Ser. No. 253,843 Claims priority, application Great Britain, Feb. 9, 1962, 5,120/ 62 6 Claims. (Cl. 313-109) This invention relates to electric discharge lamps having envelopes of the kind in which two members at least one of which is wholly or mainly of vitreous material, are sealed together, at least one of the members being shaped to provide, when assembled with and sealed to the other member, a sinuous path for an electric discharge between electrodes located at the ends of the sinuous path. The discharge lamps with which the invention is mainly concerned are fluorescent lamps, wherein the light emission arises from the excitation of a layer of luminescent material provided on the inner wall of the envelope by radiation emitted from the discharge between the electrodes, although the invention is also applicable to discharge lamps in which the visible radiation arises solely from the discharge between the electrodes.

Envelopes for electric discharge lamps of the character with which the invention is concerned, may be constructed from two sheet glass pressings, or from a glass pressing and a vitreous enamelled metal pressing which,

when assembled and sealed together provide a sinuous discharge path defined by internal barriers. Alternatively a vitreous enamelled metal backing plate may be shaped to provide the sinuous discharge path, and the other member which is in the form of a glass plate is placed upon the pressing and is sealed to the pressing at least at the outer rim thereof. In each case, the convolutions of the sinuous path are separated from one another by at least one barrier of metal or vitreous material. Metal vapour discharge lamps which are typical of the kind with which the invention is concerned have a metal vapour and one or more inert gases as the inclusion within the envelope. When such lamps are being operated there is a pumping action on the metal vapour due to the electric field set up by the discharge. The etfect of this phenomenon is much more noticeable when the lamp is operated on DC. or when it is a rectifying lamp, since in this case the pumping action is uni-directional and the metal vapour is concentrated towards one end of the discharge path. When this occurs the light output from the discharge is non-uniform along the length of the arc path and it is the object of the present invention to counteract this tendency.

In accordance with the present invention an electric discharge lamp having an envelope of the kind set forth has at least part of the or each integral barrier of the envelope which separates the convolutions of the discharge path formed from a porous ceramic or vitreous material which permits metal vapour to pass from one side of the barrier to the other.

The part of the internal barrier(s) which is porous ensures that the vapour pressure on one side of the porous part of the barrier(s) is approximately the same since any difference in pressure will cause a flow of vapour through the porous part tending to equalise the pressures. Itfollows that the most advantageous positions for the porous parts of the barrier(s) are those at which the pressure diiterence would normally be greatest.

The part of the or each internal barrier which is porous may be in the form of an insert of a porous ceramic or vitreous material which is mounted in a opening provided Patented June 28, 1966 ice in the non-porous barrier. The insert is preferably located, in the case where the sinuous path is in the form of substantial parallel convolutions forming the zig-zag path, in that part of the or each barrier which separates the maximum length of the discharge path. Alternatively the whole of the barrier(s) may be formed from a porous material, in which case the metal vapour could pass from one convolution to the next through any part of the barrier.

In a further embodiment of the invention one of the members which forms part of the envelope and which provides the internal barriers is formed in its entirely from a porous ceramic or vitreous material through which the metal vapour can pass and the envelope is hermetically sealed by forming a layer of non-porous ceramic or vitreous material on the outer surface of the member.

In order that the invention may be more readily understood it will now be described, by way of example, with reference to the accompanying drawing in which:

FIG. 1 is a perspective view of an electric discharge lamp in accordance with one embodiment of the invention,

FIG. 2 is a plan view of a discharge lamp in accordance with a further embodiment of the invention, and

FIG. 3 is a perspective view of part of the discharge lamp shown in FIGURE 2.

An electric discharge lamp having an envelope of the kind to which the present invention relates is shown in FIGURE 1. The envelope comprises two members 1 and 2 which are sealed together to provide a sinuous discharge path 3 between a pair of electrodes 4 which are located one on each end of the discharge path. The memher 2 is a pressing in the form of a shallow tray and is provided internally with barriers 5 which extend from opposite walls of the pressing in inter-digitated relation to define the discharge path 3. The member 1 is in the form of a fiat glass plate which is sealed along its perimeter to the upper edges of the member 2 and which engages with the upper surfaces of the internal barriers 5.

In accordance with one embodiment of the invention the pressing 2 is formed in its entirely from a porous ceramic or vitreous material which enables the metal vapour which is engaged within the envelope to pass through the internal barriers 5 to equalise any pressure difference which tends to build up along the discharge path when the lamp is energised. To prevent the metal vapour from passing through the walls of the pressing to the exterior of the envelope the outer surface of the pressing is covered with a layer 6 of a non-porous material such as a vitreous glaze. A fluorescent lamp which has an envelope as shown in FIG. 1 has at least the internal walls of the pressing 2 covered with luminescent material which is excited by radiation emitted from the discharge between the electrodes 4 when the lamp is energised.

The discharge lamp shown in FIGURE 2 has an envelope which is similar to that shown in FIGURE 1 except that the pressing 2 is formed from non-porous material and that each internal barrier 5 has at least one opening 7 formed therein which extends between adjacent convolutions of the discharge path. An insert 8 of porous vitreous or ceramic material is positioned in each opening to permit metal vapour to pass from one side of the barrier to the other but to prevent the discharge from passing therethrough. When one insert is positioned in each internal barrier, each insert is located at that part of the barrier at which the pressure difference would, in the absence of the porous insert, be greatest.

The insert may be mounted within the opening 7 in any convenient manner, but insulating refractory cement or a metal clip is conveniently employed. Referring to FIG. 3 the insert which is of sintered high alumina ceramic is in the form of a recessed cylindrical disc 10, the thickness of the edgeof which is greater than the thickness of the barrier 5. The edge of the recessed faced disc is providedwith an outwardly extending flange 11 which has a diameter greater than that of the opening 7. A circumferential groove 12 is formed in the edge of the insert and is spaced apart from the flange 11 by a distance equal to the thickness of the barrier. After the insert has been located in the opening, a metal annular clip 13 is located in the groove with its outer edge extending beyond the opening in the, barrier 5 in parallel relation with the flange 11'. The flange and the clip thus serve to prevent the insert from passing through the opening.

Providedthat porosity of theinsert is such as to permit a sufficiently high rate of flow of vapour, the light output of the lamp can be controlled to be substantially uniform over the whole length of the arc path.

What I claim is:

1. Anelectric discharge lamp comprising an envelope including two members hermetically sealed together, one of said members having at least one barrier formed on .one of said members and extending therefrom to the other member to define a sinuous discharge path within said envelope, electrodes located at respective ends of said discharge path, a metal vapour inclusion within said envelope, said one member being formed of a light-transmitting material, said light-transrnitting material being pervious to metal vapour, and a layer of light-transmitting impervious material in sealing relation with the outer surface of said one memberf t 2, An electric discharge lamp as claimed in claim 1 in which said one member is constituted by a vitreous material. i

t 3. An electric discharge lamp as claimed in claim 1 in which said one member is constituted by a ceramic mat a i 4. An electric discharge lamp as claimed in claim 1 in avhich a layer of light-transmitting non-porous material is secured in sealing relation to part of the surface of said barrier.

5. An electric discharge lamp comprising an envelope including two glass members sealed together, one of said members having a plurality of barriers formed thereon and integral therewith, said barriers extending from said one member to the other member and arranged in interdigitated relation such that the barriers define a sinuous discharge path within said envelope, electrodes located at respective ends of the discharge path, a metal vapour inclusion within said envelope, said one member having the barriers integral therewith being formed of a porous glass which permits metal vapour to pass therethrough, and a layer of non-porous glass in sealing relation with the outer surface of said one member.

6. An electric fluorescent lamp comprising an envelope including two members hermetically sealed together, one of said members having at least one barrier formed thereon and integral therewith, said barrier extending from said one member to'the other member to define a sinuous discharge path within the envelope, thermionic cathodes located at respective ends of said discharge path, a mercury vapour inclusion within said envelope,'a coating of laminescent phosphor material on the internal surfaces of the envelope, said members being formed of a glass which is porous and permits mercury vapour to pass there- .through and a layer of non-porous glass in sealing relation with the outersurface of said members.

References Cited by the Examiner UNITED STATES PATENTS DAVID J. GALVIN, Primary Examiner. GEORGE WESTBY, Examiner.

F A. ADAMS, S. A. SCHNEEBERGER,

Assistant Examiners. 

1. AN ELECTRIC DISCHARGE LAMP COMPRISING AN ENVELOPE INCLUDING TWO MEMBERS HERMETICALLY SEALED TOGETHER, ONE OF SAID MEMBERS HAVING AT LEAST ONE BARRIER FORMED ON ONE OF SAID MEMBERS AND EXTENDING THEREFROM TO THE OTHER MEMBER TO DEFINE A SINUOUS DISCHARGE PATH WITHIN SAID ENVELOPE, ELECTRODES LOCATED AT RESPECTIVE ENDS OF SAID DISCHARGE PATH, A METAL VAPOUR INCLUDING WITHIN SAID ENVELOPE, SAID ONE MEMBER BEING FORMED OF A LIGHT-TRANSMITTING MATERIAL, SAID LIGHT-TRANSMITTING MATERIAL BEING PREVIOUS TO METAL VAPOR, AND A LAYER OF LIGHT-TRANSMITTING IMPERVIOUS MATERIAL IN SEALING RELATION WITH THE OUTER SURFACE OF SAID ONE MEMBER. 